The present invention relates to constant velocity transmission joints having a male element having a plurality of arms, a female element defining a pair of facing tracks for each arm, the tracks being situated on opposite sides of the arm, and mounted on each arm, a mechanical transmission member. The mechanical transmission member is moveable along the longitudinal direction of the pair of tracks and establishes a connection with the arm that is swivelling and axially moveable along the axis of the arm. The mechanical transmission members each include a circularly symmetrical outer roller disposed between the corresponding tracks.
The invention applies in particular to constant velocity joints for motor vehicle transmissions.
In the text below, the terms xe2x80x9caxialxe2x80x9d and xe2x80x9cradialxe2x80x9d are used relative to the axis of the arm in question. Similarly, the terms xe2x80x9cinnerxe2x80x9d and xe2x80x9couterxe2x80x9d are used relative to the axis of revolution of the outer roller, said axis coinciding with that of the arm for a joint bent at a deflection angle of zero.
In the field of such joints, it is known that each arm of the male element moves relative to the corresponding pair of tracks in reciprocating translation along the axis of the arm. Those movements are inevitable because of the structural geometry of the joint. They result from the way the joint operates when there is a deflection angle between the two shafts coupled together by the joint, and they also come from the xe2x80x9coffsetxe2x80x9d phenomenon which consists in orbital movement performed by the center of the male element at a frequency which is three times the frequency of rotation of the joint.
When transmitting torque, friction causes those movements to generate an axial component of the drive force which gives rise to a reciprocating tilting force to which each outer roller is subjected, with the outside surfaces of the rollers generally being toroidal. That force tends to cause the outer roller to oscillate about its point of contact with the track on which it is running. The portion of the outside surface of the roller that is diametrically opposite its portion that is applying pressure then oscillates strongly relative to the surface of the tracks against which the roller is not applying pressure, thus reducing the transmission efficiency of the joint.
Those oscillations also generate a high level of noise which is disagreeable for the user. They also require the surface hardness of the zones of the tracks that are subject to oscillating contact with the roller to be reinforced by appropriate surface treatments, which treatments are often complex because of the shape of the female element. Finally, those oscillations run the risk of an outer roller becoming jammed at the ends of the track.
An object of the present invention is to provide a constant velocity transmission joint of the type mentioned in which any oscillating motion of the outer roller is prevented by means that are simple, thereby imparting remarkable stability to the roller.
According to the invention, this object is achieved by a constant velocity transmission joint of the type specified wherein, for each arm, the outside profile in meridian half-section of the outer roller comprises two arcs having curvature of the same sign cooperating with two substantially complementary arcs of the associated track to form two spaced-part contact zones, each contact zone defining a contact resultant that is substantially perpendicular to the axis of the outer roller.
In various embodiments of the invention, the arcs of the roller may be convex or circular. The outside profile of the roller may also be symmetrical about a midplane of the roller. In another aspect of the invention, the transmission member includes an inner ring disposed inside the outer roller and a coupling mechanism for coupling the inner ring and outer roller together. The inner ring allows only relative pivoting between the inner ring and the outer roller about a common axis of revolution, and the inner ring is mounted to swivel and slide relative to the arm. In one aspect, the inner ring is mounted to swivel inside the outer roller. In another aspect, the inner ring is mounted to slide on the arm along a common axis of revolution, and the inside surface of the roller and outside surface of the ring are spherical and substantially complementary. In another example, the inner ring is slidable relative to the outer roller along the axis of revolution of the roller, and the inner ring is prevented from moving axially relative to the arm.
In another embodiment, the outer roller includes two juxtaposed portions each presenting in meridian half-section an outside profile which includes one of the two arcs of the outer roller. In a further embodiment, each portion of the outer roller includes an inwardly-directed end shoulder on its inside face about the axis of the roller, the two shoulders defining between them, a cavity for receiving the coupling mechanism.
The invention also provides a transmission member for a constant velocity transmission joint as defined above.